What Challenges Humans Have To Face From Earth To Mars?: Part 3: Mars Bound Challenges (Planetary Science)

Previously on “What Challenges Humans Have To Face From Earth To Mars: PART 1 and Part 2“, we saw that Biswal and Annavarapu in their recent paper, discussed about the challenges, we have to face from Earth to Mars Exploration. They divided overall challenges into few categories like terrestrial and earthbound challenges which we have to face on the earth, interplanetary Challenges which we have to face on interplanetary space, Mars-bound and planetary surface challenges which we will have to face when we will gonna reach to Mars and during Mars exploration. I already discussed terrestrial and earthbound challenges and interplanetary challenges in the last part of this episodic series post. If you haven’t read those articles yet, kindly go through them first. In this article, we are going to discuss challenges associated with mars.. Biswal and Annavarapu divided it in two categories: Mars bound challenges and planetary surface challenges. They further elaborated these two challenges in sub-categories which I will gonna discuss below. So, let’s continue and start with.

III. Mars-Bound Challenges

A. Hazards of Exposure to Cosmic Radiation

Consequent to successful Mars Orbital Insertion, the Mars-bound challenges commence, as the crewed space vehicle need to strand in Mars orbit until further instructions from the ground for mission inception. Because the spaceship undergoes preliminary checks and validation of its components and communication relay system. So, during their stay in Mars orbit, the astronauts along with their spacecraft are exposed to high dosage of harmful galactic and extragalactic cosmic radiation as compared to low earth orbit. This radiation levels range from a minimum of 1.07 millisieverts per day to a maximum of 1.4 millisieverts per day (measured by MARIE experiment aboard 2001 Mars Odyssey) ultimately increasing the possibility of prolonged cancer and related diseases. The challenges and the consequences of radiation exposure were explicitly elucidated in last parts of this episodic posts and additional complication was explained in Hellweg’s paper. Hence, astronaut being sheltered under the Martian environment (on the surface of Mars) seems safer than stranding in low Mars orbit (LMO). Furthermore, Biswal and Annavarapu have graphically presented the comparison of radiation levels at both Earth and Mars orbit in Fig 17 and the amount of radiation assimilated by the astronauts depending on the duration of stay in LMO in Fig 18.

Fig 17 (left) Radiation Exposure at Earth & Mars Fig 18 (right) Comparison of Radiation Dose (Earth & Mars) © Biswal and Annavarapu

B. Hazards of Asteroid Impact

Astronauts aboard space vehicle in orbit or spacecraft orbiting the red planet have vulnerable to the hazard of an asteroid impact and damaging of spacecraft components. The asteroids sizes vary from micro to macro asteroids. These asteroids are ejected from the main asteroid belt due to the probabilistic collisional events occurring at a distance ranging from 2.4 to 3.4 AU from the Sun with a relative velocity of 5.4 to 8.0 km/sec. Larger asteroids can be mitigated or destroyed by directing into the Mars atmosphere, but the problem is with micrometeoroid or microasteroid that are travelling at a relative velocity of >10km/sec can cause severe damage to the spacecraft component: it includes rupture of spacecraft fuel tank through impact and penetration, affecting the spacesuit of an astronaut during extravehicular activity, and depleting the solar arrays and affecting the power production. However, this challenges cannot be completely eradicated, but proper attention required while fabricating the sensitive component of space vehicles (i.e., fuel tank, hardness of solar array, and glasses of life-support systems). Before initiating the interplanetary exploration missions sufficient thickness of walls of the fuel tank is considered during fabrication and before stepping out for extra-vehicular activity. The challenge of asteroid impact will continue to exist for future interplanetary missions beyond Mars as the main asteroid belt lies between Mars and Jupiter and spread up to hundreds of kilometers (approximately 150 million kilometers) in interplanetary space with asteroid size ranges from 50 to 150 km in diameter.

C. Communication and Solar Power Production

Communication: I have already discussed the challenges of the interplanetary communication system in last part of this episodic post. However, human exploration missions predominantly require advanced communication systems to guide and land the spacecraft modules safely on Mars. Because a small misstep during EDL phases my cost mission tragedy as two-way communication interlinks span about 20 to 45 minutes and unreachable throughout solar conjunctions. Hence enhanced and advanced communication system (i.e., laser-guided communication system that has been successfully demonstrated by NASA) either via Mars Telecommunication Orbiter (MTO) or real-time decisiveness is ideally recommended for crewed missions.

Distribution of Solar Irradiance © Biswal and Annavarapu

Solar Power: Power production at Mars appears to be the most strenuous task for Martian satellites since the intensity of solar irradiance evanesces from Earth to Mars shown in the Fig above. Hence for a crewed missions thousands of watts are essentially required. So larger solar arrays capable of outstretching their solar cells are preferred to meet the energy requirements to power the space vehicle and estimated power production rate is 100 watts per square meter (at a solar intensity of 588 W/m²). Further, this power option is limited during the Mars solar conjunctions when Earth and Mars are far from each other having Sun at the median point for a period of 10-15 days. Therefore, we can alternatively exploit radioisotope thermoelectric generators (RTG) to afford the basic power necessities thereby mounting the RTG at a safe distance from the crewed module with proper shielding (to avoid the effects of nuclear radiation). Data transfer rate and mean power generation capacity of some Mars spacecrafts are shown in table 4 by Biswal and Annavarapu.

© Biswal and Annavarapu

D. Planetary Clearance and Mars Atmospheric Entry

Mars Entry, Descent, and Landing is the sturdy assignment for both crewed and planetary landers due to the limitation of uncertainty in predicting the natural hindrance (prevalence of the variable environmental condition and dust storms) and EDL technology. Despite this challenge, Mars entry may disrupt the communication system and can cause damage to the landing module. Therefore, this obstacle can be eluded by reporting the crews in advance (grasped in Mars orbit) about the environmental condition forecasted by Mars relay orbiters. It ensures crew about the planetary clearance and their next move. Usually, this allows the crewed landers to perform orbital entry instead of direct entry which is considered as the safest approach and recommended for crewed landing. The path for both direct and orbital entry is shown in Fig 19. Because it reduces the entry velocity for increased ballistic coefficient and faster aerocapture, the risk of crash landing due to limited EDL period, and design flexibility. Further, it enables the crews and their landing modules for an effective preparation to plunge into the Mars atmosphere.

Fig 19 Trajectory Path for Direct and Orbital Mars Entry © Biswal and Annavarapu

In addition to this, the factors such as the geometry of aeroshell, diameter of parachute, entry velocity and ballistic coefficient pose a design and technical challenge for Mars landers. From the first landing attempt to the current state of technology, the geometry and mass factor of landers is limited to the diameter of the aeroshell (4.5m) and gross landing mass up to 0.9-ton. So we need to expand the diameter of aeroshell as well as parachute. Nevertheless, larger aeroshell requires larger payload fairing that seems to be more expensive than conventional launch vehicles. Alternatively, the aeroshell diameter can be enhanced with the use of hypersonic inflatable aerodynamic decelerator (HIAD) to cut down the terminal velocity and ballistic coefficient thereby increasing the drag force that will drastically reduce the terminal velocity for dynamic landing.

IV. Planetary Surface Challenges

A. Scientific Landing Site / Exploration Zone

Exploration zone with good scientific interest and resource determines the success and sustainability of the crewed mission on Mars. The scientific site should meet all necessities for the crews and should have affordable native resources for exploitation to keep alive the crew during extended surface stay mission. NASA has identified fortyseven candidate landing site for robotic and manned exploration. Of these Meridiani Planum seems to be the best site for first Crewed Mars landing and Base establishment. Because, it holds an ideal site for promising resources which includes the potential for water extraction, raw materials for infrastructure purposes, and minerals. Meridiani Planum is located at 50°N and 50°S with an elevation of below +2 km (MOLA). Additionally, it enables crews for practicing planetary cropping and plantation, food production with efficient solar power production as it lies near-equatorial latitude, and facilitates for accomplishing multidisciplinary scientific goals in terms of atmosphere, astrobiology and geosciences. Features and scientific interest of candidate landing site (Meridiani Planum) were completely reviewed by Clarke et al. in their paper.

B. Planetary Environment

Density of Mars Atmosphere: Due to the thin atmosphere of Mars, the planet is incapable of shielding its surface from being exposed to harmful cosmic radiation and pose a threat to the living astronaut on the surface. Similarly, its lean atmosphere with lower density forbids lander modules from faster aerocapture thereby limiting the EDL period. In addition to this, the composition of Mars atmosphere CO2 (95%) and O2 (0.17%) stands a challenge for the astronaut to breathe outside their spacesuit.

Low-Gravity Environment: Astronauts on Mars gets exposed to the low gravity environment affecting the periodic pattern of heartbeat, rate of blood flow, weakening the muscle and bone density, and physical movements. The human body takes time to adapt their internal organs to sustain their presence under low gravity environment. Hence, these issues can be managed by frequent practicing of physiotherapy and physical exercises or simulating artificial gravity on Mars.

Solar Irradiance and Power: The challenges of solar power do exist at every extremity beyond LEO. For a manned mission, this complication comes during the interplanetary voyage, stranded in Mars orbit, and on Mars surface. However, the intensity of solar irradiance weakens from orbit to the surface and the mean power production rate is about 20 watts per square meter (Source: InSight Mars Lander). Hence, the structure of extendable solar arrays can be employed for mass electricity production but instead, the nuclear thermoelectric generators (NTG) will be the ideal choice for power source on the surface (during the day and night). Furthermore, the intensity of solar irradiance influences the environmental temperature that poses a challenge against manned Mars exploration to stabilize the thermal stability and this challenge can be addressed with the application of Mars sub-surface habitats.

Temperature and Pressure: The frequency of temperature on Mars varies for every Martian year. Findings and observations from diverse spacecraft have shown that the temperature variance ranges from the lowest 120K near poles to the highest of 293K at the equator with an average of -210K. Hence at this range of temperature, the crew may experience complication in maintaining the thermal stability of both habitats and their body’s internal temperature to keep them warm against hypothermia. Contradictory to temperature the pressure varies from 400 Pa to 870 Pa according to the seasonal pattern. So, this challenge can be addressed by deploying Mars sub-surface habitat to balance the thermal stability during the day and night. Simulated graph of air density, solar flux, temperature, and pressure distribution on Mars shown in Fig 20.

Fig 20 Simulated graph of air density, solar flux, temperature, and pressure distribution on Mars
(as of Jan 2021). Image Courtesy: Mars Climate Database

C. Exploitation of Resources

The challenge associated with the exploitation of resources is locating a robust site for exploration as well as extraction. Because the distinct site is associated with divergent distribution and concentration of resources, the form at which they exist, and the quantity of contaminants from the aspect of planetary protection. Since transportation of resources from different sites to the base is limited due to the constraints in surface mobility and lack of long-range rovers. Further, the unavailability of the testbed to demonstrate and validate ISRU instruments under a critical and low gravity environment poses a technical challenge on the surface. Furthermore, the uncertainty in system reliability and integration remains the greatest challenge at the very beginning of the Mars Base foundation.

D. Base Construction and Surface Mobilization

For a limited crew member at the initial stage of colonization, the habitats and the other modules can be exported from the Earth. But for a larger number of the population, a Mars Base is required and construction of this massive base using labour force is not obvious due to the vulnerability of Martian Environment and exhaustion of limited survival resources. Hence robotic based construction is beneficial from the perspective of crew health and also in retaining survival resources. Similarly, system reliability and its extended operation in a critical environment remain inconsistency due to technical challenges such as unproven technologies in the appropriate testbed and solar power deficiency. In addition to this, base construction is supported by load transportation systems from various resource mining sites. This mode of transportation may prompt the systematic servicing and repairing of vehicles. Artist concept of Mars Base is shown in Fig 21.

E. Communication Interlink from Earth

The communication challenge is discussed earlier by me in the last part of this episodic post. But it is significant for the crew on Mars to stay tethered and updated about the mission plans. The communication interlink is interrupted during the superior solar conjunction for every synodic period. Hence this challenge can be addressed either by parking communication relay satellites on high non-kaplerian orbit to stride uninterrupted communication or Mars Telecommunication Orbiters (MTO) into Mars orbit prior to the mission expedition.

F. Ethical Challenge and its Implications

Astronauts either during their interplanetary transit or extended period of mission may encounter the serious effect of ethical challenge. Despite NASA’s policy, crew members aboard spacecraft may likely to experience the risk of in-space pregnancy due to their mental and extreme stressful situation throughout the mission. Besides this ethical issue can put other crew members in risk due to additional requirement of survival resources, intensive care, and attention required for the new born astronaut and mother. The complexity of space environment and microgravity may cause serious health implications to mother and child and can lead to fatal state. It is still uncertain that how far this ethical challenge can be prohibited, but the prime cause for this challenge (i.e. mental stress and psychological health) can be improved to some extent with live interaction and conversation with either family members or publics on the Earth via interplanetary internet. Further, it is recommended to select the astronauts with multidisciplinary skilled and psychologically fit in terms of social abilities. And finally…

G. Space Policy and Human Civilization

Once the progression for human civilization commences, crews from various nations may encounter the political challenge concerning the conflict of interest between nations. Because human civilization nation’s appropriation of Martian land violates the space policy of 1967 “United Nations Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including Moon and other Celestial Bodies”. According to that treaty or policy, the space and the astronomical bodies over Solar system are free for research related activities to all nations without any differentiation or discrimination. But none of the astronomical body or planetary space cannot be expropriated by any nation. Therefore, Biswal and Annavarapu recommend that having a good mutual understanding and universal conflict of interest between countries will help make the civilization towards peaceful planetary exploration and permanent base establishment. Further, if we are planning for a return or round-tip, we may encounter the hazard of back contamination from the red planet as part of Planetary Protection Policy. And this challenge can be remitted with proper screening and medical checks aboard International Space Station before landing the crews on Earth.

Fig 20 Artist concept of Mars Base Establishment and Mars Base Construction (Image Courtesy: James Vaughan – NASA’s 3D-Printed Habitat Challenge) © Biswal and Annavarapu

Reference: Malaya Kumar Biswal M and Ramesh Naidu Annavarapu, “Human Mars Exploration and Expedition Challenges”, Aerospace Research Central, 2021. https://doi.org/10.2514/6.2021-0628 https://arc.aiaa.org/doi/abs/10.2514/6.2021-0628

Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us

What Challenges Humans Have To Face From Earth To Mars?: Part 2: Interplanetary Challenges (Planetary Science)

Previously on “What Challenges Humans Have To Face From Earth To Mars?: Part 1: Earth Bound Challenges”, we saw that Biswal and Annavarapu in their recent paper, discussed about the challenges we have to face from Earth to Mars Exploration. They divided overall challenges into few categories like terrestrial and earthbound challenges which we have to face on the earth, interplanetary Challenges which we have to face on interplanetary space, Mars-bound and planetary surface challenges which we will have to face on Mars. I already discussed terrestrial and earthbound challenges in the last part of this episodic post series. If you haven’t read that article yet, kindly go through it first. In this article, we are going to discuss about..

II. Interplanetary Challenges

So lets start with..

A. Trajectory Option for Mars

Guys, trajectory analysts have proposed numerous pathways for Human Mars Exploration. Biswal and Annavarapu in their paper have discussed the major two types of trajectory classes.

Fig 8 Optimized Trajectory for Human Mars Mission between 2020 and 2040 © Biswal and Annavarapu

Opposition Class: Opposition class mission is often referred to as a short-stay mission where travelling astronauts spent most of their mission time in interplanetary space (both in outbound and inbound) with a surface stay of about 30-60 days. This class of trajectory is found risky and expensive because its optimized trajectory requires more ∆v (higher energy transfer trajectory for transit back to earth) and longer duration in interplanetary space may subject to the exposure of galactic cosmic radiation. Additionally, the opposition class mission utilizes Venus flyby that highly enables the crew for closure exposure to Sun’s hazardous elements. Further, the departure delta velocity of 7.0 km/s or above may decrease the success probability of Mars orbital capture and this requires maximized backward propulsion with high energy and fuel exhaustion.

Conjunction Class: Contradictory to opposition class, conjunction class is referred to as a long-stay mission where the crew spends most of their time on Mars surface (400-600 days) than stranding in interplanetary space. Because it makes the crew exposure to galactic cosmic radiation. But due to the benefit from the alignment of the planetary position of Earth and Mars, it grasps a minimal delta velocity of 3.36 km/s to follow a minimum energy path (Hohmann’s Trajectory) for Mars vicinity thus affording the simplest way for Mars orbital capture upon Mars approach.

Trajectory Assessment: Several trajectory assessments showed that long-stay mission may expose the crew to harmful cosmic radiation. But being shielded under the Martian environment is safer than spending much time in either Mars orbit or interplanetary space. The threat of radiation exposure on Mars can be minimized by the application of Mars Sub-Surface habitats or deep space habitats. We know that a human mission to Mars is no cheaper than a conventional mission, so the long term effort can be effectively exploited by performing various scientific observations and experiments during their long stay on Mars. Because short-stay mission may limit the long term experiments. Hence, Biswal and Annavarapu recommended conjunction class trajectory is best suited for a manned mission to Mars which is cheaper, safe, and effective in all aspects as compared to the opposition class. Moreover, in case of any emergency abort, the crew can vast-off Mars and follow high energy optimal path or free return trajectories to return back to earth. Optimized trajectory for conjunction class with launch window at 2024 and 2026 is shown in Fig 8, the duration for the human-crewed mission from the 2022 launch window to 2037 is shown in Fig 9 and delta velocity required for various abort options is shown in Fig 10.

Fig 9 (left) Duration for Human Mars Mission (2020-2040). Fig 10 (right) Delta velocity requirements for abort options © Biswal and Annavarapu

B. Trajectory Correction Maneuver

Based on the study of failure analysis of conventional probes by M.K. Biswal, Biswal and Annavarapu have found that 1/4th of Mars probes encounters ignition engine issues caused as a result of the malfunction of the thermal control system. So, Mars Transit aboard a massive space vehicle via interplanetary coast may be subjected to low pressure, low temperature, and zero or microgravity environment directly affecting the zero-boil-off temperature of the cryogenic fuel and fuel pressurization systems. Therefore, improper fuel management and temperature imbalance may result in the inappropriate firing of thrusters plighted for mid-course or trajectory correction and maneuvering. Moreover, employing a larger delta velocity during the Earth departure stage may have serious concerns over trajectory correction and maneuvering of a massive space vehicle. Hence, proper fuel management and optimal delta velocity may curtail these challenges.

C. Spaceship Management

Spaceship management and maintenance are some of the most challenging tasks for voyaging astronauts. Because of being under the microgravity and space radiation environment, the physical health of the astronauts may limit their access to the complete space vehicle and management. As we know that, the hardware and electronic equipment are the prime components advancing the space vehicle design and it gets degraded by the effect of long term exposure of harmful galactic cosmic radiation. This stands the most challenging quest for the crew aboard the spaceship. Hence, the construction of space vehicles with durable stuff (that are tested and validated in our groundbased laboratories with exposure to artificial radiation) and robust electronics are eminently endorsed. Further, it is desirable to employ artificial intelligence-based automated robots for complete management of the space vehicle to minimize the effort of the manual management system and manual detection of damaged or malfunctioned components.

D. Effect of Radiation and Zero-Gravity

Radiation: Radiation and zero-gravity are the confronting challenges of human and interplanetary spaceflight. Astronauts have a greater threat of exposure to galactic and solar cosmic rays (GCR and SCR), and solar particle events (SPE). These are the natural phenomena spontaneously anticipating from our Milky Way galaxy and deep space and a threat to spaceflight safety and security systems. NASA has categorized the serious issues of GCR and SCR exposure into four human diseases. This includes carcinogenesis, cardiovascular disease as part of tissue degeneration, lifetime risks to the central nervous system, and acute radiation syndromes. So the health consciousness of the crew is very much significant for a successful manned mission.

Fig 11 and 12 Levels of Radiation Exposure during Interplanetary Transit to Mars © Biswal and Annavarapu

In addition to this space, radiation can cause serious unrecoverable impairment of electronic components and hardware of space vehicles that might result in mission loss. Hence, sufficient thickness of radiation suit and sterling radiation shield is considered to avoid damage and degradation of the onboard circuitry system. It is because interplanetary spaceflight to Mars takes an average of 180-270 days manoeuvring the Hohmann’s transfer trajectory may expose to harmful galactic cosmic radiation in the order of 1.16-1.18 millisieverts (extremely in opposition class trajectory due to additional requirements of Venus flyby). The level of radiation exposure to the number of days is shown in Fig 11 and 12 by Biswal and Annavarapu.

Zero-Gravity/Microgravity: On a Human excursion to Mars, astronauts will experience three sorts of gravitational fields where one is during the interplanetary transit between planets, second is on the surface of Mars, and finally the third when they return back to earth. These three sorts of transition from distinct gravitational fields and zero-gravity can cause discord in brain coordination and functions, improper balance and orientation affecting the spatial orientation of brain, and motion sickness. NASA had performed various experiments aboard International Space Station (ISS) to understand the changes and impact of zero-gravity on the human body. The results showed that astronauts experience osteoporosis (bone density collapse due to the loss of bone minerals). Besides these concerns, inadequate ingestion of significant consumables and irregular exercise might result in loss of muscle strength and endurance.

Scientific Observation of Health caused by Zero-gravity: An analysis from the Space Shuttle, Mir Program, and ISS Expedition mission showed that the crew experienced serious effects on their muscle system, bones, and cardiovascular activity. After returning from the Space station crew had additional issue of improper blood pressure and blood circulation to the brain that displays the challenge in rehabilitation. But for the astronaut on a mission to Mars will remain in microgravity and zero-gravity environment over transit duration 180-270 days and may cause serious health issues. Hence sufficient countermeasures should be taken into consideration and the best way to confront this challenge is simulation or generation of artificial gravity on the spaceship. Further adequate food habitation and regular exercise will help make the astronauts remain fit and healthy throughout the mission.

E. Solar Irradiance and Temperature

Solar irradiance plays a crucial role in power generation and temperature regulation during interplanetary transit to Mars. Lower solar irradiance would reduce the solar array output required for powering the spaceship and its operating devices onboard modules. It is because the availability of solar irradiance or intensity of sunlight steadily decreases as we move far away from the sun shown in Fig 13. In general assumption, the solar array output reduces from 3000 watts at 1366 W/m² intensity (at Earth) to 1000 watts at 588 W/m² (at Mars) and the record is assumed as per the solar cell configuration of NASA’s Mars Reconnaissance Orbiter.

Fig 13 (left) Distribution of Solar Irradiance. Fig 14 (right) Distribution of Temperature © Biswal and Annavarapu

Corresponding to solar irradiance, the temperature of the interplanetary medium decreases by the function of inverse square law. Biswal and Annavarapu have shown the mean temperature variance of planets in Fig 14 based on the data provided by Williams et al. You can see, the temperature variance directly affects the thermal control systems of the space vehicle and proper thermal insulation is very much essential to keep astronaut warm and healthy in a hard environment. In addition to this, temperature variance also affects the fuel storage (zero boil-off and freezing), electronic components, and life support systems (for the growing plants or life aboard the spaceship).

F. Effect of Nuclear Hazards

Nuclear energy is considered as the source of power for the future of deep space exploration and transportation systems. Mars scientists and engineers have proposed to manoeuvre nuclear electric propulsion and nuclear thermal propulsion rockets (NEP, NTR) to minimize the transit duration from Earth to Mars and to enhance space vehicle for a faster mission. Since the NEP and NTR are the emerging technologies for the advanced propulsion system and a progressive stride towards interstellar transit. Furthermore, it is the only choice that can meet our strategy of stellar and deep space exploration including interplanetary transportation systems. Because the potential for solar irradiance and solar power is limited beyond Mars orbit to employ solar electric propulsion system (SEP). Nevertheless, the NEP, NTR has direct effects on crew health affecting cardiovascular tissue, increasing the risk of cancer throughout the lifetime, and hereditary diseases.

“Hence, during the construction and assembly of the space vehicle, we endorse to mount the crewed module or base far away from the nuclear reactor with adequate shielding to overcome this challenge.”

— told Biswal, lead author of the study

G. Isolation and Psychological Effects

A manned mission to Mars takes an average of 2.5 to 3 years that leads to the complete state of isolation/confinement of astronauts eventually affecting the behavioural and psychological patterns. Astronauts may encounter mood and cognition issue, the risk of anxiety, depression, digestive problems, loneliness, hypo or hypertension as part of behavioural changes. Psychological changes include positive moods and relationships patterns with other crew members. A collaborative study performed by Russians and ESA’s project members entitled “Mars-500” showed an increase in positive emotions among crew members. But, according to Biswal and Annavarapu, these results may remain undesirable because the actual environment of a space vehicle during interplanetary transit cannot be simulated on Earth. So, the experiences from Mars analog research stations and Arctic research stations can be treated for planning a mission to some extent.

The experiences from the crew of International Space Station (ISS) is inconsistent because the crew on transit to Mars encounter interrupted communication with their ground and family’s relations than crew aboard ISS. But instead, they have to hold on for about 40 minutes for both transmitting and receiving a single message and hence this may lead to stressful situations and social concerns. These changes are unanticipated and are far beyond how well trained and experienced they are. Therefore, it is substantial to sort out the astronauts who are physically and psychologically fit with multiple interdisciplinary skills. In addition to this, they must be capable of managing themselves during confined and stressful situations.

H. Communication and Interplanetary Internet

Communication: Communication poses a crucial role in mission engagement and keeps the astronauts updated about the mission strategies from the ground. Identically it enhances the psychological personality of the crew and increases the success probability of mission accomplishment. The scientific demand for the human and robotic exploration missions to Mars and beyond is expanding, so high bandwidth and uninterrupted advanced communication relays are highly required. Since at a distance of 1.5 to 2.5 AU (Mars encounter and beyond) the communication interlink is limited to 24 to 40 minutes and it may not be an efficient approach to stay tethered with operating science mission orbiters and crewed space vehicles. Because human mission beyond Moon and LEO is completely new and the crew is exposed to the inexperienced environment. So it is very significant to keep the crew updated about the safety measures and their next move. Additionally, the technological unavailability of persistent communication coverage for manned vehicles (other space probes in Mars orbit or on the surface), proper interlink during superior solar conjunction, the need for simultaneous control over multiple proximity operations on Mars vehicles (Spaceships, orbiters, landers, and rovers), and the exigency to access the Deep Space Network (DSN) for current mission trends are the some of the significant challenges on the way to communication systems. Detailed Review on Advanced Communication Technologies for Human Mars Exploration and their countermeasures are explained in Bhasin et al.

Interplanetary Internet: Interplanetary Internet provides easy access to reliable scientific resources for the crew and enables the public to get updated with live coverage from interplanetary space. This mode of consistent internet and communication from the public directly to the crew may minimize the mental stress (due to good appreciation and encouragement from public interactions) thereby increasing their interdisciplinary activities. Further, interplanetary internet enables the onboard crew to perform various scientific studies or research works as part of their free time with massive access to research papers (optional assignment). The current trend of networking technology can able to accomplish an interlink transfer of ~100-2015 Mbps for downlink and ~10-25 Mbps for uplink via EarthMars trunk line and need to be upgraded for advanced communication relay. In addition to this, NASA is currently planning either to park two-three telecommunication relay orbiters in HMO or MSO to form an integrated constellation architecture for providing increased bandwidth and data transfer rate or to park in Earth-Sun Lagrangian point for deep space communication access with optical fibre and laser-guided communication system.

I. Cryogenic Fuel Management during Interplanetary Transit

Alike on-orbit or in-space refueling I discussed in last part of this episodic series post, cryogenic fuel management (CFM) is necessary during the extended presence of humans on an exploration mission to Mars, and beyond. Because propellant plays a vital role in transiting space vehicles from a point to the destination and assists in performing sturdy mid-course and trajectory correction maneuver. Nevertheless, fuel depletion may prompt in the decline of the mission and it is necessary to effectuate proper CFM procedure. Further, the future exploration mission greatly relies on three factors of the extraterrestrial based cryogenic fuel management system, they are management of cryogenic propellant (liquid hydrogen, liquid methane, liquid oxygen), storage, and distribution. As I discussed in last part, active thermal control, demonstration of cryogenic propellant management, fuel transfer, instrumentation leak detection, liquid acquisition devices, low-gravity mass gauging, passive thermal control, pressure control, refrigeration, storage, system feed testing, and zero boil-off are the key technology for fuel management.

These elements of CFM pose a substantial challenge for fuel management on the way to interplanetary transit to Mars. Efforts to address this challenges were developed in NASA’s ground-based laboratories include Cryogenic Propellant Operations Demonstrator (CPOD), Experimentation for the Maturation of Deep Space Cryogenic Refueling Technology (MDSCR), In-Space Cryogenic Propellant Depot (ISCPD), Zero Boil-Off Tank (ZBOT). Till date, accomplished CFM technology and the demand for future were clearly reviewed by Chato in his paper. Now, Biswal and Annavarapu have shown the approximate time duration required for propellant storage and technology readiness level for CFM in Fig 15 and Fig 16.

Fig 15 (left) Duration required for CFM. Fig 16 (right) Technology Readiness Level for CFM © Biswal and Annavarapu

J. Waste Recycling and Management

Long duration transit to Mars may result in the generation of large amount to trash that ultimately plunges the crew to biological and physical hazard. The entire trash generated includes exhaled CO2 gases from astronauts, used waters, human wastes, biological wastes, solid wastes, nuclear wastes, and medical wastes. Amidst these, biological, nuclear and medical waste poses a serious threat to crew and may increase the probability of crew sickness and a prolonged threat to cancer. So, the disposal of these trashes requires adequate attention and disposal procedure (anaerobic digester) with consideration of crew safety and risk. According to Lockhart, a crew of four can generate a waste of about 2.5 tons per year. In consequence manned mission to Mars for 2-3 years may result in the generation of 7.5-8 tons. Hence, the measure for recycling and reusing is an ideal approach for a sustainable interplanetary transit rather than conventional trash disposal and venting, because the cargo re-supply and availability is limited from the Earth. The current trend of recycling method followed aboard International Space Station can be further modified and enhanced to accommodate adequate waste management, water recycling, and oxygen generation during interplanetary transit to Mars.

K. Extra-Vehicular Activity

Space colonization highly necessitates the potential capabilities of hours of extravehicular activity performed by the astronaut outside their shielded spacecraft with sophisticated skills and mature technology. EVA plays a great role in accomplishing space assembly, servicing, and space vehicle management and can be extended to provide ecstatic owing to the psychological effects experienced by the astronauts during interplanetary travel. EVA requires a bounded environment in terms of pressure, temperature, and the concentration of oxygen with the additional capability of supplying water and food, temperature regulation, pressure retention, and waste collection within the suit.

But the challenges that affect EVA are direct exposure of astronauts to the galactic cosmic radiation, elements of solar flares, difficulty in balancing their momentum in zero gravity, mechanical hazards and the risk of losing in space as a result of a defective tether. In addition to this galactic particles or micro asteroids travelling with a relative velocity of 10 km/s may hit and puncture the space suit pushing into a critical situation. Further, an analysis on these challenges by Pate-Cornell grouped the overall EVA challenges into eight categories namely failure of airlock and life support system, fire in the suit, mechanical and radiation accident, separation, spacesuit failure, and de novo events. Hence, astronaut equipped with good EMU (Extravehicular Maneuvering Unit) suit may reduce the risk of losing in space. Moreover, healthy space suit with high tolerance (when exposed to vacuum environment) and multiple capabilities can increase the robustness and longevity of EVA. The suit should be developed concerning the experiences encountered by EVA astronauts aboard ISS and other human spaceflight program. Furthermore, NASA’s Johnson Space Center is currently involved in the development of Robonaut (Robotic astronaut’s assistant) that can enhance the efficiency of EVA hours with improved capabilities of strength, dexterity, and mobility.

L. Mars Approach and Orbit Capture

Once we vast-off from the Earth, the next destination is approaching Mars. Accurate targeting and successful Mars Orbital Insertion (MOI) thereby diminishing the delta velocity is very significant for a successful mission. Because, once the space vehicle remains ineffective in capturing orbit, it is very difficult to maneuver back the spaceship to its destination point. As I discussed earlier in last part, the factors such as the delta velocity, fuel management, proper functioning of navigation, maneuvering, and ignition system determines the success probability of Mars Orbital Insertion. However, many inexperienced robotic spacecraft like ESA’s Mars Express and ISRO’s Mars Orbiter Mission (MOM) has successfully demonstrated excellent Mars Orbital Capture in their first attempt. But, in the case of the crewed mission, it is extremely recommended that experiences and lesson learned from past successful Mars probes can be doubtlessly applied for orbital capture. Since inaccurate targeting, timing, and malfunction of breaking engine could pose the space vehicle stranded in interplanetary space or could cause the vehicle destroyed in Mars atmosphere and mission tragedy.

So that’s all about interplanetary challenges.. We will discuss final challenge associated with Mars on last part of this series..

Reference: Malaya Kumar Biswal M and Ramesh Naidu Annavarapu, “Human Mars Exploration and Expedition Challenges”, Aerospace Research Central, 2021. https://doi.org/10.2514/6.2021-0628 https://arc.aiaa.org/doi/abs/10.2514/6.2021-0628

Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us

What Challenges Humans Have To Face From Earth To Mars?: Part 1: Earth Bound Challenges (Planetary Science)

Space exploration has diverse challenges and the exploration of Mars possess numerous challenges whereas the Mars exploration has been a source of inspiration to global space firms for decades. The inspiration for Mars began from the conceptual and architectural designs first put forwarded by Wernher von Braun. To date, we have extensively demonstrated numerous space technologies efficient for executing human class missions to Mars and beyond. Similarly, we have successfully explored the red planet with numerous autonomous spacecrafts and planetary probes. So, from the perspective of sustainable and efficient human-crewed mission, it is substantial to consider the natural challenges caused by the phenomena of the space environment and technological challenges ensued from the artificial technologies and that’s what Biswal and Annavarapu studied in their paper. They have studied and emphasized every possible challenge that the crew may experience during their interplanetary spaceflight from the Earth to the Mars except the Entry, Descent, and Landing challenges, as it was already technically reviewed by R.D. Braun. They stratified overall challenges into terrestrial, earthbound, interplanetary, Mars-bound, and planetary challenges under the simplified categorization of terrestrial, interplanetary, and planetary challenges outlined in Fig 1 below.

Fig 1 Outline Map for Human Mars Exploration and Expedition Challenges © Biswal and Annavarapu

Let’s start with..

I. Terrestrial Challenges

A. Consideration of feasible future technology

From the perspective of efficient human-crewed Mars mission, it is significant to consider simple, robust, feasible, and affordable future technologies. Don’t suspect researchers assumptions towards extreme or massive technology but to have substantial technology that can be engineered with our existing pieces of machinery. (For example: if we propose to use SEP (Solar Electric Propulsion) for the space transportation system, we might be having hardship in fabricating massive solar panels, enfolding together to place in LEO with the launch vehicle and deploying in interplanetary space. Further, the challenge for this type of propulsion system is the availability of solar irradiance for powered propulsion that gradually decreases as we move far apart from the sun with a variance of 1360 W/m² (at Earth) to 590 W/m² (at Mars). Alternatively, Electric Propulsion, NTR, NEP, and NIMP for transit to Mars can be exploited with the technology of controlled propulsion and management. It minimizes the risk of mass constraints.

Similarly, other than powerful propulsion systems, we need to develop and demonstrate advanced inflatable heat shield to ground large scale masses, power spacesuits to keep the astronauts safe against hostile Mars environment, the concept of sub-surface habitats to maintain thermal stability and the habitat on wheels to enable surface mobilization, uninterrupted power generation employing radioisotope thermoelectric generators or fission power systems, and advanced laser-guided communication system to stay tethered from Earth to receive more information and to stay updated about the mission strategies.

B. Mission Design and Architecture Selection

Mars enthusiasts and scientists have proposed more than 70 human Mars mission’s architectures since 1952. Analyzing through hundreds of pages, comparing with feasible technologies, and executing the mission plan with the right budget seems complicated. Because each and every proposal have their desired goal. So it is preferable to sort out simple, robust with economic standard and feasible plans. Hence, Biswal and Annavarapu have selected (12) architectural strategy for budget comparison and reliability shown in Fig 2.

Fig 2 Mission Architecture and Estimated Cost (in Billion USD). © Biswal and Annavarapu

Among these strategies, SpaceX’s Mars expedition, Mars One, NASA’s Design reference mission has the potential technology to attempt for a human-crewed mission to Mars within the time frame of 2040 and 2060s. Further, based on the current state of matured technology, these strategies were found to be feasible and inexpensive as compared to other mission plans.

C. Consideration of the Heavy Lift Launch Vehicle

The primary progression step towards the Mars expedition is the launch of heavy mass (cargoes, crews, and necessities) to low earth orbit (LEO) as part of initial mass low earth orbit (IMLEO). Delivering of large mass facilitates the reliability of mission thereby expanding the number of cargoes required for the crews and planetary exploration, size of the crew, and possible payloads for spaceship rendezvous in low earth orbit (LEO). But the technology of launch vehicle to deliver large scale mass has made a significant impact to execute a mission. Numerous architectures on launch vehicle enhancement were proposed like Soviet Union’s N1 Rocket, Aelita, United States Saturn MLV, Comet HLLV, Ares, Sea Dragon, and SpaceX’s Interplanetary Transportation System. These launchers may have the potential to deliver huge IMLEO mass with an extent from 100-1400 metric tons. But the task of construction, launch, testing, and validation may cost expensive and infeasible. Hence technologically feasible launchers such as Saturn V, Ares V, SLS, Falcon Heavy, Long March, Starship, New Glenn are considerable for manned mission. It is because some are under development and some are technologically proven in past decades. Moreover, if these launchers come accessible, they can lift a mass variant from 40-200 metric tons to LEO and may pave a way for the affordable human class Mars MISSION. In fig 3, Biswal and Annavarapu showed launchers and their respective payload mass to LEO and launch cost comparison.

Fig 3 Launch Vehicles and their payload capacity to LEO. © Biswal and Annavarapu

D. Crew Size Limitation

The most crucial part of the Human Mars Expedition is the commission of crew and crew size that determines the extent of mission accomplishment. The size of the crew defines the quantity of cargoes desired over the mission period that affecting the initial mass (IMLEO) allocated for launch. Comparably a limited number of crew influences the state of psychological fitness and the ability to accomplish the scientific goal. So it is substantial to sort out each crew with multitudinous skills (For example a crew capable of accomplishing his/her assigned work along with the skill of medical first aid, managing spaceship, rectifying the damaged instruments and miscellaneous). It is always desirable to have stability between the crew and the commodity. Hence, Biswal and Annavarapu interpreted that the limit of crew size from 4 to 6 seems to be ideal for mission robustness.

E. Simulated Training of Crew

Before executing human class Mars mission in a challenging space environment, the astronaut (future Martians) undergoes a various and complex process of sub-orbital training to validate the rate of mission accomplishment during their stay in mission. For this intention, various space and Mars firms have effectuated human analog missions to simulate various environmental aspects. Some of the human Mars analog training centers with their locations and objectives are shown in table 1.

© Biswal and Annavarapu

It is worth and satisfactory to have testing, validation, and training in a planetary simulated environment. But the results are incomparable to the actual space environment. Because some results may go erroneous. In a longduration space mission, the first and foremost priority must be given to the crew safety and surviving requirements. For every emergency, there must be a back-up plan and mission abort option that can be proceeded. We cannot put life at risk on a voyage of the search for life. It is not that the mission can be accomplished without crew, instead, it is with the crew. It is significant to make avail every crew necessity at a remote distance.

II. Earth-Bound Challenges

A. Hazards of Space Debris

The prevalence of sub-orbital space debris of variable sizes around earth rises the potential danger to all space missions and vehicles. There are the circumstances where the spacecraft experiences collision with the debris and can lead to the Kessler Syndrome. NASA Keeps tracking the debris and data of sub-orbital debris with the aid of the Department of Defense and Space Surveillance Network. Employing the data Joint Space Operation Center contribute to the interpretation of conjunction assessment to meet the human spaceflight criteria thereby reporting to the Johnson Spaceflight Center and Goddard Space Flight Center. Even though debris is carefully tracked, the threats come as a result of untraced debris of small sizes. For the manned mission, we need to launch and strand large seized orbital vehicles in LEO and have an increased chance of vulnerability to sub-orbital debris. Nations and their quantity of debris are shown in Fig 4.

Fig 4 Space Debris by Nations © Biswal and Annavarapu

B. Spaceship Rendezvous

In the scenario of the manned Mars mission, we need to launch an enormous number of spaceship segments into LEO to enable the assembly of Crew Transportation Vehicle. Launching a massive space vehicle aboard launchers is unsustainable due to the limitation of launch vehicle technology to assemble a transportation vehicle for Mars excursion. Hence the assembly requires refined orbital rendezvous and docking technology. We have successfully demonstrated this technology in the 1960s when Gemini 6A and Gemini 7 achieved a technological milestone. Since 1960 astronauts have gone through manual rendezvous (during Apollo and Shuttle Program) and automatic rendezvous (during ISS mission) by making use of Radar (Radio Detection and Ranging) and Lidar (Light Detection and Ranging) technology. And the Lidar has a better insight into future docking and proximity operations. Further, focusing on manual and autonomous rendezvous, both can be preferred in LEO (but autonomous is best). But in the case of Mars orbital rendezvous, autonomous proximity operations and docking is always preferred than manual method (considering the risk of crew safety and health fitness). Because a small misstep can lead to mission loss and space disaster. So, according to the statement of Dr. Dennehy (NASA GNC Technical Fellow) “Autonomous rendezvous and capture will be an integral element of going to Mars”, it is absolute fact and for this, Biswal and Annavarapu recommended to execute autonomous rendezvous and proximity operations in Mars orbit than manual.

C. Orbital Refueling

Refueling of space vehicles and reusing of vented tanks or launcher components are the key technology of manned mission to drive the cost down. In refueling operations, significant criteria like fluid transfer, pressure control, pressurization, gauging, zero-boil off storage, mixing desertification, passive storage, and leak detection are to be considered for fuel management. The low gravity in space greatly influences the Deep Space Refueling process. Additionally, the technology of fluid transfer, liquid acquisition, and mass gauging have a low technology readiness level and need to be matured. So, we need to conduct more experiments and enhance refueling technology despite past experiments shown in table 2.

© Biswal and Annavarapu

D. Recycle and Reusable Technology

Currently, we have extended our technology to reuse the launch vehicle components (For example Past space shuttle – first reusable launch system). To date, several space firms have demonstrated the reusable technology. Some of them were tabulated by Biswal and Annavarapu in table 3. Considering economic standard and low-cost space access, we need to extend and enhance the reuse and fabrication technology to space vehicles, fuel tanks, and degraded satellites (solar panels, batteries, and some reliable components).

© Biswal and Annavarapu

E. On-Orbit Construction and Assembly

On-Orbit constructions and assembly are one of the greatest challenges for future deep space exploration mission as well as Mars expedition. The manual on-orbit assembly has numerous threats and challenges like the effect of zero-gravity on physical health, exposure to solar irradiance, solar flare and eruptions, cosmic radiations, dynamics of astronauts, health, and energy aspects. Space firms like NASA, ROSCOSMOS, ESA are involved in developing artificial intelligence robots for on-orbit constructions to redress the above challenges. Hence for future missions (where large spaceships and space platforms are required), robotic on-orbit constructions assure 100% safe and secure assembly eliminating every on-orbit challenges. Levels of radiation exposure are shown by Biswal and Annavarapu in Fig 5.

Fig 5 Levels of Radiation Exposure on Earth & Mars (Image Courtesy: JPL/NASA)

F. Achieving maximum delta-v (∆v)

Achieving maximum delta velocity (∆v) relies on possible orbit-raising maneuvers with the aid of chemical thrusters (thruster fairing on-off), gravity assist, and advanced propulsion system. Exploiting chemical propulsion systems, we can achieve a minimal delta velocity of 5.08 km/s (variable) and may take up to 180 days to transit from Earth to Mars. Longer transit time has increased exposure of crew to hazardous space environmental conditions. However, exploiting the most preferred approach of NTR (Nuclear Thermal Rocket or Propulsion) proposed in many human mission architectures with maximum delta velocity of 8 km/s can minimize the transit time to 120-130 days approximately. The transit time and delta-velocity relation are shown in Fig 6 by Biswal and Annavarapu and it shows the increase in delta velocity decreases the interplanetary transit time from Earth to Mars.

Fig 6 Delta Velocity and Transit time to Mars © Biswal and Annavarapu

G. Mars Trajectory

We have several trajectory options and are classified into conjunction class and opposition class. Beneficial human class mission requires more scientific goals and its extent of accomplishment. So conjunction class trajectory is more favourable than the opposition class trajectory. Because conjunction class has Mars surface stay time of approx. 350 days higher than the opposition class approx. 30 days and it minimizes the crew exposure to galactic cosmic radiation and solar flares being sheltered under the Martian environment. Opposition class trajectory has maximum exposure to cosmic hazard throughout Trans-Mars as well as Trans-Earth transits due to shorter surface stay period and additional requirement of Venus flyby (that makes closure vulnerability to the Sun and its hazardous elements). Opposition class mission increases the mission budget parallel to launch mass and propulsive energy, but in case of conjunction class mission – it follows the least energy path with minimal energy requirement (Hohmann’s Transfer Trajectory). Hence, conjunction class mars mission is decidedly recommended for Human Mars Expedition and it is found to be the most proposed approach in various mission strategies. Comparison of the duration of crew exposed to various states of Mars expedition (both Conjunction and Opposition class trajectory) is shown in Fig 7 by Biswal and Annavarapu.

Fig 7 Comparison of Trajectory Class © Biswal and Annavarapu

So that’s all about challenges we have to face on Earth.. We will discuss further challenges in next part of this series..

Reference: Malaya Kumar Biswal M and Ramesh Naidu Annavarapu, “Human Mars Exploration and Expedition Challenges”, Aerospace Research Central, 2021. https://doi.org/10.2514/6.2021-0628 https://arc.aiaa.org/doi/abs/10.2514/6.2021-0628

Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us

Introducing The Most Energetic Flare Star Of the Decade, “GT Mus” (Planetary Science / Astronomy)

A team of international astronomers reported that the RS CVn-type star GT Mus (HR4492, HD 101379+HD 101380) was the most active star in the X-ray sky in the last decade in terms of the scale of recurrent energetic flares. Their study recently appeared in Astrophysical Journal.

MAXI is an all-sky X-ray monitor that has been operating on the Japanese Experiment Module (JEM; Kibo) on the International Space Station (ISS) since 2009 August 15. It observes a large area of the sky once per 92 minute orbital cycle and makes it possible to search for transients effectively.

Among the MAXI-detected stellar flare sources, the RS CVn-type star GT Mus showed remarkably energies flared with energies up to ~ 1038 erg repeatedly. So far, MAXI has detected flare candidates with the MAXI “nova-alert system” designed to detect transients from MAXI all-sky images in real time.

The quadruple system GT Mus (HR4492) consists of two binary systems named HD 101379 and HD 101380, located at (R.A., Dec.)(J2000) = (11h39m29s.497, −65°23’52”.0135) at a distance of 109.594 pc. The two binaries (HD 101379 and HD 101380) are separated by 0.23 arcsec, which is spatially resolved by speckle methods.

The RS CVn-type single-lined spectroscopic binary HD 101379 has a G5/8 giant primary with a radius of 16.56 R. This binary shows strong CaII H, CaII K, and variable Hα emissions. Moreover, it shows a periodic photometric variation of 61.4 days, which dominates any other variations of GT Mus. This 61.4 day variation may be attributed to a rotational modulation of one or more starspots on HD 101379. These features indicate high magnetic activity, which implies that the flare observed by MAXI may have originated on HD 101379.

The other system, HD 101380, is a binary consisting of an A0 and an A2 main-sequence star. In the folded V-band GT Mus light curve, a small dip is detected. It is interpreted to be due to an eclipse of this binary with a period of 2.75 day. No variations by spots have ever been observed. Thus, it is feasible to speculate that HD 101379 has higher chromospheric activity than HD 101380.

All of the reported MAXI flares from GT Mus so far have been detected by the MAXI “nova-alert system”. However, there is a real potential that some flares have been missed by this automated system. Given the current small number (23) in the MAXI stellar flare sample and the highly active nature of GT Mus, GT Mus provides a good opportunity to study the physical characteristics of stellar flares and their mechanism.

Now, Sasaki and colleagues carried out a detailed analysis of the MAXI data of GT Mus to search for Xray flares. They successfully detected 11 flares (including the three that have been already reported) in 8 yr of observations with Monitor of All-sky X-ray Image (MAXI) from 2009 August to 2017 August. All flared showed a total released energy of 1038 erg or higher. They also performed a unified analysis for all of them and found that the detected flare peak luminosities were 1–4 × 1033 erg s¯1 in the 2.0–20.0 keV band for its distance of 109.6 pc.

Their timing analysis showed long durations (τr +τd) of 2–6 days with long decay times (τd) of 1–4 days. The released energies during the decay phases of the flares in the 0.1–100 keV band ranged 1–11 × 1038 erg, which are at the upper end of the observed stellar flare. The released energies during whole duration time ranged 2–13 × 1038 erg in the same band.

They also carried out X-ray follow-up observations for one of the 11 flares with Neutron star Interior Composition Explorer (NICER) on 2017 July 18 and found that the flare cooled quasi-statically. On the basis of a quasi-static cooling model, the flare loop length is derived to be 4 × 1012 cm (or 60 R). This size is a 2–3 orders of magnitude larger than that of the typical solar flare loop of 109–1010. While, the electron density is derived to be 1 × 1010 cm¯3, which is consistent with the typical value of solar and stellar flares (1010¯13 cm¯3). The ratio of the cooling timescales between radiative cooling (τrad) and conductive cooling (τcond) is estimated to be τrad ∼ 0.1 τcond from the temperature; thus radiative cooling was dominant in this flare.

Figure 1. Scatter plot of the X-ray to bolometric luminosity ratio (LX/Lbol) vs. Rossby number (Ro). Dots and plus signs are for late-type main-sequence single and binary stars, respectively. The solar symbol is for the Sun. Squares are for G- and K-type giant binaries. The star indicates GT Mus. © Sasaki et al.

Furthermore, for the first time, they plotted the G and K giant binary samples in the diagram of X-ray to bolometric luminosity ratio versus Rossby number (shown in fig 1) and obtained a consistent distribution with those for the low-mass stars. The Rossby number and log(LX/Lbol) of GT Mus are 0.614 and −3.5, respectively, which puts GT Mus in line with the relation derived from low-mass and giant binary stars in the diagram. It shows a considerably higher LX/Lbol than other giant binaries. This high X-ray fraction suggests that GT Mus is at a high magnetic activity level, which is consistent with what is inferred from its recurring large flares.

Featured image: R/B-band color composite image of GT Mus from the Second Digitized Sky Survey (DSS2), measuring 30 arcminutes across. © In-the-Sky

Reference: Ryo Sasaki, Yohko Tsuboi, Wataru Iwakiri, Satoshi Nakahira, Yoshitomo Maeda, Keith C. Gendreau, Michael F. Corcoran, Kenji Hamaguchi, Zaven Arzoumanian, Craig Markwardt, Teruaki Enoto, Tatsuki Sato, Hiroki Kawai, Tatehiro Mihara, Megumi Shidatsu, Hitoshi Negoro, Motoko Serino, “The RS CVn type star GT Mus shows most energetic X-ray flares throughout the 2010s”, the Astrophysical Journal, 910(1), 23 Mar 2021. https://iopscience.iop.org/article/10.3847/1538-4357/abde38

Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us

Why We Prefer Concave Shape Inflation Potential Rather Than Convex? (Cosmology / Quantum / Maths)


⦿ There are two types of inflation potential we generally prefer: Concave and convex. The Planck data on cosmic microwave background indicates that the Starobinsky-type model with concave inflation potential is favored over the convex-type chaotic inflation. But why? This reason is still unclear.

⦿ Now, Chen and Yeom investigated Euclidean wormholes in the context of the inflationary scenario in order to answer the question on the preference of a specific shape of the inflaton potential.

⦿ They argued that if our universe began with a Euclidean wormhole, then the Starobinsky-type inflation is probabilistically favored.

⦿ They showed that only one end of the wormhole can be classicalized for a convex potential, while both ends can be classicalized for a concave potential. The latter is therefore more probable.

⦿ Their study point towards the fact that its not the universe but the wormhole which is expanding

How did the universe begin? This has long been one of the most fundamental questions in physics. The Big Bang scenario, when tracing back to the Planck time, indicates that the universe should start from a regime of quantum gravity that is describable by a wave function of the universe governed by the Wheeler-DeWitt (WDW) equation. The WDW equation is a partial differential equation and hence it requires a boundary condition. This boundary condition allows one to assign the probability of the initial condition of our universe. As is well known, to overcome some drawbacks of the Big Bang scenario, an era of inflation has been introduced. Presumably, the boundary condition of the WDW equation would dictate the nature of the inflation.

The Planck data on cosmic microwave background (CMB) indicates that certain inflation models are more favored than some others. In particular, the Starobinsky-type model with concave inflation potential (V” < 0 when the inflation is dominant.) appears to be favored over the convex-type (V” > 0) chaotic inflation. Is there any reason for this? Now, Chen and Yeom argued that if our universe began with a Euclidean wormhole, then the Starobinsky-type inflation is probabilistically favored.

One reasonable assumption for the boundary condition of the WDW equation was suggested by Hartle and Hawking, where the ground state of the universe is represented by the Euclidean path integral between two hypersurfaces. The Euclidean propagator can be described as follows:

where gµν is the metric, φ is an inflaton field, SE is the Euclidean action, and h (Sys. (a,b), stat. (µν)) and χ^a,b are the boundary values of gµν and φ on the initial (say, a) and the final (say, b) hypersurfaces, respectively. Using the steepestdescent approximation, this path integral can be well approximated by a sum of instantons, where the probability of each instanton becomes P ∝ e^−S_E. This approach has been applied to different issues with success: (1) It is consistent with the WKB approximation, (2) It has good correspondences with perturbative quantum field theory in curved space, (3) It renders correct thermodynamic relations of black hole physics and cosmology. These provide Chen and Yeom the confidence that the eventual quantum theory of gravity should retain this notion as an effective description.

FIG. 1: Complex time contour and numerical solution of ar, ai, φr, and φi for Vch. The upper figure is a physical interpretation about the wormhole, where Part A (red) and C (green) are Lorentzian and Part B (blue) is Euclidean. © Chen and Yeom

In their original proposal, Hartle and Hawking considered only compact instantons. In that case it is proper to assign the condition for only one boundary; this is the so-called no-boundary proposal. In general, however, the path integral should have two boundaries. If the arrow of time is symmetric between positive and negative time for classical histories, then one may interpret this situation as having two universes created from nothing, where the probability is determined by the instanton that connects the two classical universes. Such a process can be well described by the Euclidean wormholes.

Now, Chen and Yeom investigated Euclidean wormholes in the context of the inflationary scenario in order to answer the question on the preference of a specific shape of the inflaton potential. They showed that only one end of the wormhole can be classicalized for a convex potential, while both ends can be classicalized for a concave potential. The latter is therefore more probable.

“We investigated Euclidean wormholes with a non-trivial inflaton potential. We showed that in terms of probability, the Euclidean path-integral is dominated by Euclidean wormholes, and only the concave potential explains the classicality of Euclidean wormholes. This helps to explain, in our view, why our universe prefers the Starobinsky-like model rather than the convex-type chaotic inflation model.

— told Chen, first author of the study

It should be mentioned that there exist other attempts to explain the origin of the concave inflation potential. For example, it was reported by Hertog in his paper that, the Starobinsky-like concave potential is preferred if a volume-weighted term is added to the measure. Chen and Yeom note that the same principle can be applied not only to compact instantons but also to Euclidean wormholes; hence, this proposal may support their result as well. They must caution, however, that the justification of such a volume-weighted term is theoretically subtle.

This is of course not the end of the story. One needs to further investigate whether this Euclidean wormhole methodology is compatible with other aspects of inflation. It will also be interesting to explore the relation between the probability distribution of wormholes and the detailed shapes of various inflaton potentials. Furthermore, if this Euclidean wormhole creates any bias from the Bunch-Davies state, then it may in principle be confirmed or falsified by future observations. They left these topics for future investigations.

Featured image: Comparing the inflation models with the observational constraints. © Ke Wang

Reference: Chen, P., Yeom, Dh. Why concave rather than convex inflaton potential?. Eur. Phys. J. C 78, 863 (2018). https://doi.org/10.1140/epjc/s10052-018-6357-0 https://link.springer.com/article/10.1140/epjc/s10052-018-6357-0

Copyright of this article totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us

A Single Injection Reverses Blindness in Patient with Rare Genetic Disorder (Medicine)

Penn Medicine researchers have found that a mutation-specific RNA therapy improved vision with lasting effects

A Penn Medicine patient with a genetic form of childhood blindness gained vision, which lasted more than a year, after receiving a single injection of an experimental RNA therapy into the eye. The clinical trial was conducted by researchers at the Scheie Eye Institute in the Perelman School of Medicine at the University of Pennsylvania. Results of the case, detailed in a paper published today in Nature Medicine, show that the treatment led to marked changes at the fovea, the most important locus of human central vision.

The treatment was designed for patients diagnosed with Leber congenital amaurosis (LCA) — an eye disorder that primarily affects the retina — who have a CEP290 mutation, which is one of the more commonly implicated genes in patients with the disease. Patients with this form of LCA suffer from severe visual impairment, typically beginning in infancy.

“Our results set a new standard of what biological improvements are possible with antisense oligonucleotide therapy in LCA caused by CEP290 mutations,” said co-lead author Artur V. Cideciyan, PhD, a research professor of Ophthalmology. “Importantly, we established a comparator for currently-ongoing gene editing therapies for the same disease, which will allow comparison of the relative merits of two different interventions.”

In an international clinical trial led at Penn Medicine by Cideciyan and Samuel G. Jacobson, MD, PhD, a professor of Ophthalmology, participants received an intraocular injection of an antisense oligonucleotide called sepofarsen. This short RNA molecule works by increasing normal CEP290 protein levels in the eye’s photoreceptors and improving retinal function under day vision conditions.

A Penn Medicine patient with a genetic form of childhood blindness gained vision, which lasted more than a year, after receiving a single injection of an experimental RNA therapy into the eye. Visual function at the eye’s foveal cone photoreceptors improved slowly, reaching a substantial peak near three months after the injection. Graphic courtesy of Artur V. Cideciyan created with BioRender.com.

In a 2019 study published in Nature Medicine, Cideciyan, Jacobson, and collaborators found that injections of sepofarsen repeated every three months resulted in continued vision gains in 10 patients. The eleventh patient, whose treatment was detailed in the latest Nature Medicine paper, received only one injection and was examined over a 15-month period. Prior to treatment, the patient had reduced visual acuity, small visual fields, and no night vision. After the initial dose, the patient decided to forgo the quarterly maintenance doses, because the regular dosing could lead to cataracts.

After a single injection of sepofarsen, more than a dozen measurements of visual function and retinal structure showed large improvements supporting a biological effect from the treatment. A key finding from the case was that this biological effect was relatively slow in uptake. The researchers saw vision improvement after one month, but the patient’s vision reached a peak effect after month two. Most striking, the improvements remained when tested over 15 months after the first and only injection.

According to the researchers, the extended durability of vision improvement was unexpected and provides implications for treating other ciliopathies — the name of the large category of diseases associated with genetic mutations encoding defective proteins, which results in the abnormal function of cilia, a protruding sensory organelle found on cells.

“This work represents a really exciting direction for RNA antisense therapy. It’s been 30 years since there were new drugs using RNA antisense oligonucleotides, even though everybody realized that there was great promise for these treatments,” said Jacobson. “The unexpected stability of the ciliary transition zone noted in the patient prompts reconsideration of dosing schedules for sepofarsen, as well as other cilium-targeted therapies.”

 One reason why antisense oligonucleotide has proven successful in treating this rare disease, according to the researchers, is that these tiny RNA molecules are small enough to get into the cell nucleus, but are not cleared very quickly, so they remain long enough to do their work.

“There are now, at least in the eye field, a series of clinical trials using antisense oligonucleotides for different genetic defects spawned by the success of the work in CEP290-associated LCA from Drs. Cideciyan and Jacobson,” said Joan O’Brien, MD, chair of Ophthalmology in the Perelman School of Medicine and director of the Scheie Eye Institute

For future studies, the Penn authors are planning gene-specific therapies for other currently incurable blinding inherited retinal disorders.

Additional Penn authors included: Alexandra V. Garafalo, Alejandro J. Roman, Alexander Sumaroka, Arun K. Krishnan, and Malgorzata Swider.

The trial is being funded by ProQR Therapeutics with additional support from the National Institutes of Health.

Reference: Cideciyan, A.V., Jacobson, S.G., Ho, A.C. et al. Durable vision improvement after a single treatment with antisense oligonucleotide sepofarsen: a case report. Nat Med (2021). https://doi.org/10.1038/s41591-021-01297-7 (2) Cideciyan, A.V., Jacobson, S.G., Drack, A.V. et al. Effect of an intravitreal antisense oligonucleotide on vision in Leber congenital amaurosis due to a photoreceptor cilium defect. Nat Med 25, 225–228 (2019). https://doi.org/10.1038/s41591-018-0295-0

Provided by Penn Medicine

Copper Foam as a Highly Efficient, Durable Filter For Reusable Masks and Air Cleaners (Material Science)

During the COVID-19 pandemic, people have grown accustomed to wearing facemasks, but many coverings are fragile and not easily disinfected. Metal foams are durable, and their small pores and large surface areas suggest they could effectively filter out microbes. Now, researchers reporting in ACS’ Nano Letters have transformed copper nanowires into metal foams that could be used in facemasks and air filtration systems. The foams filter efficiently, decontaminate easily for reuse and are recyclable.

When a person with a respiratory infection, such as SARS-CoV-2, coughs or sneezes, they release small droplets and aerosolized particles into the air. Particles smaller than 0.3 µm can stay airborne for hours, so materials that can trap these tiny particles are ideal for use in facemasks and air filters. But some existing filter materials have drawbacks. For example, fiberglass, carbon nanotubes and polypropylene fibers are not durable enough to undergo repeated decontamination procedures, while some further rely on electrostatics so they can’t be washed, leading to large amounts of waste. Recently, researchers have developed metallic foams with microscopic pores that are stronger and more resistant to deformation, solvents, and high temperatures and pressures. So, Kai Liu and colleagues wanted to develop and test copper foams to see if they could effectively remove submicron-sized aerosols while also being durable enough to be decontaminated and reused.

The researchers fabricated metal foams by harvesting electrodeposited copper nanowires and casting them into a free-standing 3D network, which was solidified with heat to form strong bonds. A second copper layer was added to further strengthen the material. In tests, the copper foam held its form when pressurized and at high air speeds, suggesting it’s durable for reusable facemasks or air filters and could be cleaned with washing or compressed air. The team found the metal foams had excellent filtration efficiency for particles within the 0.1-1.6 µm size range, which is relevant for filtering out SARS-CoV-2. Their most effective material was a 2.5 mm-thick version, with copper taking up 15% of the volume. This foam had a large surface area and trapped 97% of 0.1-0.4 µm aerosolized salt particles, which are commonly used in facemask tests. According to the team’s calculations, the breathability of their foams was generally comparable to that of commercially available polypropylene N95 facemasks. Because the new material is copper-based, the filters should be resistant to cleaning agents, allowing for many disinfection options, and its antimicrobial properties will help kill trapped bacteria and viruses, say the researchers. In addition, they are recyclable. The researchers estimate that the materials would cost around $2 per mask at present, and disinfection and reuse would extend their lifetime, making them economically competitive with current products.

The authors acknowledge funding from the Georgetown Environmental Initiative Impact Program Award, the McDevitt bequest to Georgetown University and Tom and Ginny Cahill’s Fund for Environmental Physics at University of California Davis.

Featured image: A copper-based foam filter that could someday be used in facemasks or air cleaners sits on the bristles of a plant, illustrating its light-weight nature. Credit: Adapted from Nano Letters 2021, DOI: 10.1021/acs.nanolett.1c00050

Reference: James Malloy et al. “Efficient and Robust Metallic Nanowire Foams for Deep Submicrometer Particulate Filtration”
Nano Letters, 2021.

Provided by American Chemical Society

New Target Identified to Develop Treatment for Abdominal Aortic Aneurysm (Medicine)

An abdominal aortic aneurysm (AAA) is a bulging of the aorta, the body’s main blood vessel, which runs from the heart down through the chest and stomach. Prevalence of AAA in the population is high, up to nearly 13% depending on age group, particularly for men aged 65 and over. An AAA can get bigger over time and rupture, causing life-threatening bleeding. There is a high mortality rate of around 80% in patients with ruptured AAA; only dropping to around 50% when patients undergo surgery.  

While clinicians can monitor the beginnings of AAA, a rupture can occur suddenly without warning. Currently, the only available intervention involves a high-risk surgical procedure, which is only undertaken if there is a real danger of rupture. There are no pharmacological treatment options because the underlying causes of AAA are not fully understood.   

Scientists know that in some patients there is a genetic predisposition to AAA, and large genomic studies have identified that mutations in a large protein called LRP1 predispose people to aortic aneurysm, as well as other major vascular diseases. However, the mechanism responsible for how these mutated genes cause the disease has so far been unknown.  

Vascular smooth muscle cell differentiation is essential to the development of healthy blood vessels. The smooth muscle cells of the aorta play a crucial role in maintaining its stability and protecting it against disease. In their healthy contractile state, they provide strength and produce the elastin proteins to withstand forces and assist with pumping blood around the body. In disease, damage to the lining of the aorta causes accumulation of fat and allows immune cells to infiltrate vessel walls. In response, the vessel attempts to repair itself and the smooth muscle cells try to make more smooth muscle. However, in doing so, the cells start to de-differentiate and become less contractile.

“They undergo proliferation, presumably with good intentions to try and make more smooth muscle, but actually it makes the problem worse.”

According to Associate Professor of Cardiovascular Development and Regeneration Nicola Smart: ‘They undergo proliferation, presumably with good intentions to try and make more smooth muscle, but actually it makes the problem worse. In doing so, they also break down the elastic layers of the heart that keep the vessels stable. These layers are supposed to hold the whole vessel together, keep it tight and keep it strong, and it all breaks apart.’

Comparing a healthy aorta with what it looks like in the event of an aneurysm © University of Oxford

But why do the smooth muscle cells react in this way? Professor Smart’s research group has found that a small protein called Thymosin b4 (Tb4) is working alongside the larger LRP1 protein to determine how many ‘growth factor receptors’ are sent to the cell’s surface to respond to disease. If Tb4 is absent, then instead of being destroyed, too many receptors are recycled back to the cell’s surface, which makes the smooth muscle cells hyper-sensitive and in essence overreact.

Professor Smart’s team then compared their results with AAA samples from the Oxford Abdominal Aortic Aneurysm study. The OxAAA team surgically repair aneurysms in human patients, removing diseased tissue from the lining of the abdomen in the process. Through examining these samples, the Smart group were able to confirm that Tb4 and LRP1 interact in both healthy and diseased patient vessels. Consequently, their study sheds light on a key regulatory step in AAA and Tb4 has been identified as a promising new drug target to potentially treat the disease. 

More details can be found in The Journal of Clinical Investigation.

Featured image: Comparing a healthy aorta with what it looks like in the event of an aneurysm © University of Oxford

Reference: Sonali Munshaw, … , Keith M. Channon, Nicola Smart, “Thymosin β4 protects against aortic aneurysm via endocytic regulation of growth factor signaling”, Information: J Clin Invest. 2021. https://doi.org/10.1172/JCI127884

Provided by University of Oxford

Beneficial Bacteria Help Wheat Stand the Heat (Agriculture)

Coating crop seeds with bacteria found on a desert shrub boosts yields in hot fields.

Video: Researchers at KAUST have identified bacteria that can boost heat tolerance in wheat. The team’s bacteria-bolstered wheat had up to 50% higher yields than normal. © 2021 KAUST; Anastasia Serin.

Bacteria plucked from a desert plant could help crops survive heatwaves and protect the future of food.

Global warming has increased the number of severe heatwaves that wreak havoc on agriculture, reduce crop yields and threaten food supplies. However, not all plants perish in extreme heat. Some have natural heat tolerance, while others acquire heat tolerance after previous exposure to higher temperatures than normal, similar to how vaccines trigger the immune system with a tiny dose of virus.

But breeding heat tolerant crops is laborious and expensive, and slightly warming entire fields is even trickier.

Heribert Hirt (left) and Kirti Shekhawat (right) are exploring ways to help achieve sustainable agriculture by harnessing microbes to protect plants. © 2021 KAUST; Anastasia Serin

There is growing interest in harnessing microbes to protect plants, and biologists have shown that root-dwelling bacteria can help their herbaceous hosts survive extreme conditions, such as drought, excessive salt or heat.

“Beneficial bacteria could become one of the quickest, cheapest and greenest ways to help achieve sustainable agriculture,” says postdoc Kirti Shekhawat. “However, no long-term studies have proven they work in the real world, and we haven’t yet uncovered what’s happening on a molecular level,” she adds.

To fill this knowledge gap, Shekhawat, along with a team led by Heribert Hirt, selected the beneficial bacteria SA187 that lives in the root of a robust desert shrub, Indigofera argentea. They coated wheat seeds with the bacteria and then planted them in the lab along with some untreated seeds. After six days, they heated the crops at 44 degrees Celsius for two hours. “Any longer would kill them all,” says Shekhawat.

The team believe thousands of other bacteria have the power to protect plants against diverse threats, from droughts to fungi, and are already testing some on other crop types.  © 2021 KAUST; Anastasia Serin

The untreated wheat suffered leaf damage and ceased to grow, while the treated wheat emerged unscathed and flourished, suggesting that the bacteria had triggered heat tolerance. “The bacteria enter the plant as soon as the seeds germinate, and they live happily in symbiosis for the plant’s entire life,” explains Shekhawat.

The researchers then grew their wheat for several years in natural fields in Dubai, where temperatures can reach 45 degrees Celsius. Here, wheat is usually grown only in winter, but the bacteria-bolstered crops consistently had yields between 20 and 50 percent higher than normal. “We were incredibly happy to see that a single bacterial species could protect crops like this,” says Shekhawat. 

The team then used the model plant Arabidopsis to screen all the plant genes expressed under heat stress, both with and without the bacteria. They found that the bacteria produce metabolites that are converted into the plant hormone ethylene, which primes the plant’s heat-resistance genes for action. “Essentially, the bacteria teach the plant how to use its own defense system,” says Shekhawat.

Thousands of other bacteria have the power to protect plants against diverse threats, from droughts to fungi, and the team is already testing some on other crops, including vegetables.  “We have just scratched the surface of this hidden world of soil that we once dismissed as dead matter,” says Hirt. “Beneficial bacteria could help transform an unsustainable agricultural system into a truly ecological one.”

Featured image: Studies have shown that root-dwelling bacteria can help plants and crops survive extreme conditions, such as drought, excessive salt or heat. © 2021 KAUST; Anastasia Serin


  1. Shekhawat, K., Saad, M.M., Sheikh, A., Mariappan, K., Al-Mahmoudi, H., Abdulhakim, F., Eida, A.A., Jalal, R., Masmoudi, K. & Hirt, H. Root endophyte induced plant thermotolerance by constitutive chromatin modification at heat stress memory gene loci. EMBO reports 22 (2021).| article

Provided by KAUST